J DICK1, P GAN1, M ALIKHAN1, R KITCHING1, S HOLDSWORTH1
1Monash University , Clayton , Australia
Aim: To determine the potential of low dose IL-2 therapy in experimental ANCA-associated vasculitis (AAV).
Background: Low dose IL-2 expands regulatory T cells (Tregs) and is a potential therapy for autoimmune disease.
Methods: Anti-MPO autoimmunity was induced in C57BL/6 mice by immunisation with MPO. T cell mediated anti-MPO glomerulonephritis was triggered on day 16 in immunised mice by anti-GBM globulin, and MPO-ANCA induced glomerulonephritis by passive transfer of MPO-ANCA/LPS. Mice were treated with IL-2, 25,000units/day for 7 days. Immune responses were measured by flow cytometry, ELISPOT and ELISA.
Results: IL-2 increased splenic Tregs (26.2±0.8vs17±0.3 %CD4+, P<0.0001) and up-regulated expression of the suppressive markers CTLA4 and PD-1. Mice treated with IL-2 before MPO immunisation developed attenuated Th1 and Th17 autoimmunity, measured by splenocyte ELISPOT (IFN-γ 68±12vs123±16 spots, P=0.009; IL-17A 31±7vs70±12 spots P=0.003). This was associated with reduced segmental glomerular necrosis (24±4vs48±6%, P=0.0054) and reduced albuminuria. IL-2 pre-treatment did not alter humoral immunity.Treatment with IL-2 before passive transfer of MPO-ANCA/LPS increased numbers of intra-renal Tregs (2316±402vs1246±170 CD4+Foxp3+cells/kidney, P=0.02) and reduced intra-renal F4/80hiCCR2hi inflammatory macrophages (P<0.01).To evaluate therapy in established autoimmunity, mice were treated with IL-2 12 days after MPO immunisation. Although splenic Tregs were expanded, T effector response was also enhanced with more IFN-γ and IL17A producing cells (both P<0.01). Conversely, IL-2 therapy attenuated ANCA production (0.49±0.04 vs 0.29±0.03 OD480, P=0.0019), this was associated with suppressed T follicular helper cell generation. The net effect of IL-2 therapy was exacerbation of glomerular necrosis (87±3vs26±4%, P<0.0001) and increased albuminuria.
Conclusions: IL-2 has diverse and context specific effects on cellular and humoral autoimmunity. The potentiation of T effector responses in established autoimmunity may limit its utility in AAV.
Dr Jonathan Dick studied medicine at the University of Oxford and University College London before training in internal medicine and nephrology in London. He recently completed a PhD at Monash University supervised by Professors Steve Holdsworth and Richard Kitching on novel roles for complement in pre-clinical models of ANCA-vasculitis.